Basophil – Definition, Structure, Functions

Basophils are an immunological cell type that release enzyme-containing granules during allergic responses and asthma crises. Basophil is a type of white blood cell that, together with neutrophils and eosinophils, belongs to the granulocytes category.

They contain several chemicals, including histamine and heparin. As part of the body’s immune response, basophils degranulate (split open) to release these chemicals after an allergic reaction. These cells serve a variety of activities to safeguard our bodies, and there are a number of diagnostic tests available to determine the extent of any damage or disease we may be experiencing.

What are Basophils?

• Granulocytes and Agranulocytes are the two types of white blood cells, commonly known as leukocytes, based on the presence or lack of granules.
• Granulocytes include neutrophils, eosinophils, and basophils, which contain granules.
• Granulocytes collaborate to treat diseases or allergies in the human body. Each type of granulocyte contains a distinct combination of chemicals and enzymes within its granules.
• Basophils are the smallest granulocytes, with a diameter of 10 to 14 m.
• These polymorphonuclear cells contain a bilobed nucleus and highly metachromatic cytoplasmic granules.
• They only live for one to two days.
• These are the only histamine-containing leukocytes that circulate in the body.

Structure of Basophils

• When basophils are labelled, their enormous cytoplasmic granules hide the cell nucleus under the microscope. However, when the nucleus is unstained, its two lobes are typically visible.
• Another granulocyte with a similar look and function is the mast cell.
• Both cell types store the chemical histamine, which is produced by activated cells.
• Mast cells, however, originate from separate branches of hematopoiesis and are typically found in connective tissue rather than the bloodstream.
• When necessary, basophils, like other circulating granulocytes, can be recruited from the blood into a tissue.

Development of Basophils

• In the bone marrow, these cells grow alongside neutrophils and eosinophils. It is believed that a basophil has a maximum lifespan of 70 hours.
• Basophils originate from a shared progenitor cell with eosinophils and neutrophils.
• It is not understood how basophils differentiate from other cell types, however the emergence of IL-3 appears to correspond with this process.
• It has been demonstrated that IL-3 promotes the development of bone marrow precursor cells. In contrast to mast cells, human basophils circulate and may be drawn to locations of an inflammatory response, but will not be identified in normal tissue.
• Basophils originate from hemopoietic stem cells influenced by a myeloid progenitor.
• Development will proceed in the bone marrow or spleen as a pre-basophil/mast cell progenitor.
• Basophils are discharged into the bloodstream, where they await stimulation by an allergen or other stimulus.
• They can also be activated by immunoglobulin, cytokines, or other growth factors, as well as bacteria or bacterial subparticles, particularly in the case of parasites, viruses, or allergies.

Microscopic (histologic) description

• Basophilic granules are metachromatic (reddish purple) and water-soluble with Toluidine blue and Alcian blue.
• Basophilic myeloblast: difficult to differentiate from other granulocyte blasts; big, spherical cells with basophilic cytoplasm and no granules; N/C ratio of 80%. scattered chromatin including nucleolus
• Basophilic promyelocyte: developmental intermediate between basophilic myeloblast and myelocyte; big, circular cell with undifferentiated cytoplasmic granules; Slight chromatin clustering, presence of nucleolus
• Basophilic myelocyte: Basophilic myelocytes are often larger than neutrophilic granules. N/C ratio is fifty percent; moderately compacted chromatin; no distinct nucleolus
• Basophilic metamyelocyte: oval cell with abundant pale cytoplasm, big and rather uniform specific granules; N/C ratio of 40%; tiny, indented nucleus with condensed chromatin; absence of nucleolus.
• Basophil: smaller than normal white blood cells (10 – 15 microns); cytoplasm is pale blue but frequently hidden by purple blue granules (carrying heparin and histamine); N/C is 20%; nucleus is frequently unsegmented or bilobed, chromatin is coarse.

Action of Basophils

• Basophils contribute to the activation of inflammatory reactions.
• Inflammation is the body’s natural response to anything that could be harmful.
• It is the body’s way of instructing the immune system to mend and restore damaged tissues while defending against foreign invaders.
• Histamine and heparin are among the chemicals present in basophil granules.
• Function of Histamine: It is a vasodilator, meaning it widens blood vessels. This draws additional immune cells to the damaged or infected area.
• Function of Heparin: It has anti-coagulant properties (blood thinner). The body produces it to prevent blood clots from forming at the site of an injury or infection.
• Additionally, basophils indirectly target foreign agents by binding to B-cell lymphocytes.
• As a result of the binding, B-cells release antibodies known as immunoglobulin E (IgE) into the bloodstream.
• IgE possesses potent anti-parasite and anti-venom properties.

Basophils Role in Allergies

• An allergy occurs when the immune system reacts abnormally to an otherwise harmless chemical or event.
• The release of histamine by basophils is one of the primary causes of allergy symptoms.
• When the body is exposed to allergens, basophils and similar cells called mast cells burst open (allergy-causing chemical).
• Histamine causes blood arteries to widen, allowing surrounding tissues to receive fluid.
• As these tissues expand and become inflamed, they can cause skin inflammation, redness, and itching in the form of rashes and hives.

Levels of Basophils – Normal Range of Basophils

• The concentration of white blood cells, of which basophils comprise between 0.5 and 1 percent, is determined by a test called a white blood cell (WBC) count.
• Absolute basophil count (ABC) is a test that measures the precise amount of basophils in millilitres (mm3).
• The usual range for basophils is 0.5% to 1% of the total white blood cell count. This corresponds to zero to 300 basophils per microliter of blood in healthy humans.
• If your basophil count exceeds this threshold, you may be suffering from allergic responses, chickenpox, collagen vascular disease, hyperthyroidism, or bone marrow illness.
• Cancer, acute infection, and thyrotoxicosis are denoted by a decrease in basophils.
• Blood testing may reveal elevated or depleted levels of basophils in response to particular illnesses or treatments.
• Basophilia is characterised by an abnormally high basophil count, and basopenia is characterised by an abnormally low basophil count.

Diseases related to high basophil counts

• Allergic reactions: Basophils are involved in the immune response to allergens, so a high basophil count may be seen in people with allergies or allergic reactions.
• Parasitic infections: Basophils play a role in fighting parasitic infections, so a high basophil count may be seen in people with these types of infections.
• Chronic myelogenous leukemia: This is a type of cancer that can cause an increase in the number of basophils in the blood.

Diseases related to low basophil counts

There is not a specific disease that is caused by a low count of basophils, but a low count can be a sign of an underlying health condition. In some cases, a low count of basophils may be related to a problem with the bone marrow or immune system.

For example, a low count of basophils can occur in myelodysplastic syndromes, a group of disorders that affect the production of blood cells in the bone marrow. It can also occur in some types of leukemia, such as acute lymphocytic leukemia or chronic myelogenous leukemia.

In addition, a low count of basophils may be a side effect of certain medications, such as corticosteroids, which are often used to treat inflammatory conditions such as asthma and rheumatoid arthritis.

If you have a low count of basophils, your healthcare provider will likely want to do additional testing to determine the underlying cause. Treatment will depend on the underlying condition and may include medications, such as growth factors or immune-modulating drugs, or more intensive therapies, such as chemotherapy or bone marrow transplantation.

How do Basophils work against pathogens? (Immunity)

• The granulocyte-monocyte progenitor cells of the bone marrow differentiate into basophils, which are then released into the peripheral blood as fully differentiated cells.
• The transcription factor C/EBPα is required for the differentiation of precursor cells into the basophil lineage.
• Under normal conditions, the number of basophils in the blood remains constant, but increases in response to parasitic infections or allergies.
• The exact nature of the stimuli responsible for basophil development during parasitic infections remains unclear, but the cytokine IL-3 from the hematopoietic system has been implicated as playing a crucial role.
• Other parasite-associated molecules, such as proteases, glycoproteins, or structural components such as chitin, can also stimulate basophil differentiation.
• Basophils, like mast cells, are activated by the cross-linkage between the surface IgE receptor, FcεRI, and blood-borne IgE antibodies.
• The binding of IgE to basophils results in the activation of intracellular mediators, such as histamine and leukotrienes. The increased concentration of these compounds causes basophils to secrete more cytokines, such as IL-4.
• In addition, IL-4-independent pathways involving IL-3 that result in basophil activation have been described.
• Activated basophils produce a substantial quantity of IL-4, which may even exceed that of T cells.
• The basophil-produced IL-4 induces the differentiation of parasite-specific naive T cells into Th2 effector T cells.

Causes of Low count of basophil

There are several possible causes of a low count of basophils, also known as basopenia. Some of the most common causes include:

1. Corticosteroid use: Corticosteroids are medications that are commonly used to treat a variety of inflammatory conditions, such as asthma and rheumatoid arthritis. However, they can also lower the number of basophils in the blood.
2. Radiation therapy: Radiation therapy, which is used to treat cancer, can damage the bone marrow and lead to a decrease in the number of basophils.
3. Myelodysplastic syndromes: Myelodysplastic syndromes are a group of disorders that affect the bone marrow’s ability to produce enough healthy blood cells, including basophils.
4. Blood cancers: Certain types of blood cancers, such as acute lymphocytic leukemia and chronic myelogenous leukemia, can cause a decrease in the number of basophils.
5. Autoimmune disorders: Some autoimmune disorders, such as lupus and rheumatoid arthritis, can cause a decrease in the number of basophils.
6. Infections: In some cases, certain types of infections can cause a decrease in the number of basophils, although this is less common.

Causes of Low count of basophil

A high count of basophils, also known as basophilia, can be caused by several different factors. Here are some of the most common causes:

1. Allergic reactions: Basophils are involved in the immune response to allergens, so a high basophil count may be seen in people with allergies or allergic reactions.
2. Parasitic infections: Basophils play a role in fighting parasitic infections, so a high basophil count may be seen in people with these types of infections.
3. Chronic myelogenous leukemia: This is a type of cancer that can cause an increase in the number of basophils in the blood.
4. Inflammatory disorders: Some inflammatory disorders, such as ulcerative colitis and rheumatoid arthritis, can cause a high basophil count.
5. Stress: Stress can trigger the release of certain hormones that can cause a temporary increase in the number of basophils.
6. Thyroid disorders: Some thyroid disorders, such as hypothyroidism, can cause a high basophil count.
7. Certain medications: Certain medications, such as heparin and certain types of antibiotics, can cause a high basophil count.

Method of basophil count

Basophil count is typically measured through a complete blood count (CBC) test, which is a routine blood test that measures various components of the blood, including the number of basophils.

To perform a basophil count, a healthcare provider will take a small sample of blood, usually from a vein in the arm. The blood sample is then sent to a laboratory for analysis.

In the laboratory, the blood sample is analyzed using an automated machine that counts the number of different types of blood cells, including basophils. The results of the CBC test are reported as a number of cells per microliter of blood.

The normal range for basophil count is usually between 0 and 2% of the total white blood cell count. However, the specific normal range may vary slightly depending on the laboratory and the person’s age, gender, and overall health.

If the basophil count is outside of the normal range, further testing may be needed to determine the underlying cause. This may include additional blood tests or other diagnostic tests, such as bone marrow biopsy.

Function of Basophils

• Basophils are one of five types of white blood cells that protect the body against infection and respond to foreign invaders such as parasites, fungi, and cancer cells.
• They are part of the innate immune system, which is the immunity present at birth.
• Basophils are responsible for regulating the human body’s reaction to allergens.
• When we come into contact with allergens, we experience sneezing, coughing, and runny nose.
• Early-stage cancer cells can be identified and eliminated.
• Basophils also release histamine from their granules during an allergic reaction or asthma attack, which plays a key role.
• In addition, they protect our bodies from microbiological diseases, viruses, parasites, etc.
• They are essentially the first line of defence against any foreign agent that enters the body.

References

• Sticco KL, Pandya NK, Lynch DT. Basophilia. [Updated 2022 Oct 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK535365/
• https://www.medicalnewstoday.com/articles/324188
• https://www.verywellhealth.com/what-are-basophils-797206
• https://www.sciencedirect.com/topics/engineering/basophil
• https://www.pathologyoutlines.com/topic/bonemarrowbasophils.html
• https://www.oatext.com/the-basophil.php
• https://www.akadeum.com/types-of-cell-separation/granulocyte-isolation-from-whole-blood-types-of-granulocytes-and-granulocytes-function/what-are-basophils-leukocyte-isolation-and-leukopak-processing-with-bacs/
• https://www.thermofisher.com/in/en/home/life-science/cell-analysis/cell-analysis-learning-center/immunology-at-work/granulocyte-cell-overview/basophil-overview.html
• https://www.healthline.com/health/basophils#what-happens-if-yourlevel-is-high

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